How to Build a Chainable Filter Helper in Python

from dataclasses import dataclass
from typing import Callable, Iterator, Sequence, TypeVar

T = TypeVar("T")


@dataclass
class FilterAssistant:
    """Beginner-friendly helper to filter any collection."""

    data: Sequence[T]

    def where(self, predicate: Callable[[T], bool]) -> "FilterAssistant":
        return FilterAssistant([item for item in self.data if predicate(item)])

    def first_n(self, n: int) -> "FilterAssistant":
        return FilterAssistant(self.data[:n])

    def unique(self) -> "FilterAssistant":
        seen = set()
        result = []
        for item in self.data:
            if item not in seen:
                seen.add(item)
                result.append(item)
        return FilterAssistant(result)

    def apply(self) -> list:
        return list(self.data)


if __name__ == "__main__":
    numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 3, 7]
    result = (
        FilterAssistant(numbers)
        .where(lambda x: x % 2 == 0)
        .where(lambda x: x > 2)
        .unique()
        .first_n(3)
        .apply()
    )
    print(result)